This invention relates to determining the characteristics of ultrashort laser pulses and, more particularly, the application of electronic devices for measuring parameters that completely characterize ultrashort laser pulses.
The development of ultrashort, i.e., picosecond and sub-picosecond, laser sources has largely precluded techniques for the accurate and complete characterization of the pulses coming from such lasers. Currently, the most commonly used measurement is the non-linear correlation. Unfortunately, this autocorrelation provides only an estimate of the pulse width, and contains no information about the specific amplitude and phase of the pulse.
Methods that lead to the determination of the phase and amplitude of the pulse include iterative fitting on an interferometric autocorrelation and the pulse spectrum, or generating asymmetric interferometric correlations with the insertion of quadratic dispersion in one arm of the correlator. More recent techniques involving higher order nonlinearities, combined with numerical algorithms, have been successfully introduced. While these techniques work well, they generally require high intensity pulses.
It should be noted that the common element in all of the measurements mentioned above is an optical nonlinearity with a femtosecond response time. Unfortunately, broadband nonlinearities are generally weak and require very intense ultrashort pulses. Some compromise between bandwidth and the magnitude of the nonlinear response can be made through the use of a phase matched crystal. In practice, however, a different crystal has to be used for different laser wavelengths. In view of this, there exists a need for an electronic device that covers a broad range of wavelengths. Initial work in this direction has been demonstrated in Li et al., "2-picosecond GaAs photodiode optoelectronic circuit for optical correlation applications," 61 Appl. Phys. Lett., pp. 3104-3106 (1992). A GaAs Schottky photodiode monolithically integrated with a microwave detector was used to perform correlations of picosecond optical pulses for time domain measurements on a train of laser pulses.
It is an object of the present invention to extend the temporal resolution of the GaAs Schottky photodiode monolithically integrated with a microwave detector to the ultrashort (picosecond to femtosecond) regime when used in a frequency domain measurement.
Another object of the present invention is to directly measure the amplitude and phase of an ultrashort laser pulse using only an integrated optoelectronic circuit.
One other object of the present invention is to determine the amplitude and phase of a single non-repetitive laser pulse using a two-dimensional integrated optoelectronic circuit.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.